Piezo-electric device



A. M L. NICOL$ON PIEZO ELECTRIC DEVICE Jan. 10, 1928.

2 Sheets-Sheet 2 Original Fi-l'efl Feb. 28, 1925 //7/ e/770r.' A/ lander/V1 /V/6'0/J0/Z p my Patented Jan. 10, 1928.

UNETED STATES 1,655,625 PATENT OFFICE.

ALEXANDER MoL. NICOLSON, OF NEW YORK. N. Y. ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.. A CORPORATION OF NEW YORK.

PIEZO-ELECTRIC DEVICE.

Application filed February 28, 1928, Serial No. 621,704. Renewed March 19, 1927.

This invention relates to transforming one form of energy into another where one ofthe forms of energy is the energy of electric current waves, and especially where the other form of energy is the energy of sound waves.

An object of the invention is an efiicient means for accomplishing such transforma tions, either of electrical energy to inechanical energy or vice versa, and especially an eflicient .piezo-electric loud speaking telephone receiver.

In, accordance with the invention a piezoelectric structure and adiaphragm or the like are so associated that elastic strains of the structure will be accompanied by motion of the diaphragm. Elastic vibrations may be set up in the piezoelectric structure by the application thereto of electric forces, for example forces due to voice currents. The pieZo-electric structure may be formed of crystals so arranged that the displacements in a plurality of the crystals areintegrated for application to the diaphragm. or so arranged that the stress exerted on the diaphragm by a plurality of the crystals is the summation of the stresses exerted by the individual ones of these crystals, or so arranged that both the displacements and the stresses are thus integrated. The diaphragm may be so associated with the crystal structure as to be operated by twisting of the structure, which is preferably attached to a base having an inertia large in comparison to the resistance that the diaphragm offers to being vibrated, so that the vibrations of the crystal structure are citiciently transmitted to the diaphragm. The instrument is reversible asregards its functioning, so that if the diaphragm be vibrated by forces external to the instrument, for instance by forces due to sound waves in air, the crystal structure will generate electromotive force waves corresponding to the vibrations of the diaphragm.

Fig. 1 is a front view of a form of the invention employing but two crystals. with the diaphragm removed; Fig. 2 is a side elevation of this form of the invention, with the diaphragm partly broken away; F ig. 3 is a front view of a form of the invention employing two pairs of crystals: Fig. 4 is a diagrammatic plan View indicating the arrangement of the two pairs of crystals in the structure of Fig. 3; Fig. 5 is a similar diagrammatic plan view indicating a different arrangement of crystals; Fig. 6 is a front view of a modification'of the structure of Fig. 1 employing a closed container for the crystals, the diaphragm being partly broken away; Fig. 7 is a plan view of the form of the invention shown in Fig. 6, with the dia phragm removed; Fig. 8 is a sectional elevation of a form of the invention employing a watch case form of mounting for the crystals; and Fig. 9 is a front view of Fig. 8, with the diaphragm and the horn removed.

Referring especially to Figs. 1 and 2, a piezo-electric structure 10 is formed of two crystals 11 and 12, one secured on top of the other, the structure being attached to'a base 13. A channel bar 14 secured to the top of the crystal 11 carries a diaphragm 15. The crystals 11 and 12 are preferably sodium potassium'tartrate crystals made in the form described in my article on the piezoelectric effect in the composite rochelle saltcrystal, published in the Proceedings of the American Institute of Electrical Engineers, November, 1919, and by the process described in my Patent No. 1,438,965, December 19, 1922, piezo-electric devices and methods of producing the same.

As pointed out in the A. I. E. E. article just referred to, each crystal has two end poles or poles of like sign, the basal planes perpendicular to the principal axis, i. e., the axis. of the. cr vstal-aud has an equatorial or girdle pole of the. opposite sign orthogonal. thereto comprising the remaining faces of the crystal. As the crystals are shown in Figs. 1 and 2, their C axes coincide and are vertical. Thus, 16 is the upper basal plane of crystal 11, 17 is the lower basal plane of crystal 11, 18 is the upper basal plane of crystal 12, and 19 is the lower basal plane of crystal 12. The vertical faces of the crystal 11 are electrically connected together by a girdle electrode 20 which may be a strip of tinfoil wrapped about a crystal to form a loop or band having as its axis the principal axis of the crystal. A lead 21 is brought from the girdle electrode 20, the drawing showing one end. 22, of lead 21 wrapped'several times around the girdle electrode 20. Similarly, the vertical faces of crystal 12 are electrically connected together by a girdle electrode 23, from which is brought a lead 24.

The base 13 is shown as circular, and may llll ' i be, for instance, of cast iron, preferably grooved as shown at 25, to 'receive'the lower endof crystal 12. The crystal is secured in the groove preferably-by cement 26, made,

if desired, by melting crystalline sodium po-.' The fused mass may be meshes of the grid, then holds very securely.

A lead 28 is brought oil from electrode 27'; and leads 29 and 30 are brought oli' from the channelobar 14 and the base '13 respectively, the channel bar, as well as the base,

being of electricallyconducting material,

T he

such'for instance as a suitable metal. diaphragm 15'is preferably conical and of fibrous material such, .for example, as paper, with the' periphery of the diaphragn'i free but turned back to form an annular groove as at 31. ,This turned back periphery assists the diaphragm to maintain its shape -when the reaction of theanr tends to strain it. The apex of the diaphragm is secured to the channel .bar 14 by means of a short rod 32 having a shoulder 33 which abuts against'one side of the bar 14, the rod carrying a nut 34 which screws against the othpiyside of, bar 14. The shorter. the part of the-rod 32 between the shoulder 33 and the apex. of the diaphragm, the less will be its inertia and its maxunum deformation, and therefore the better will be the opera- I tion of the device.

In the operation of the device as a-loudspeaking receiver it is ordinarily preferable to connect leads 2L and Ql-to one pole and leads 28 and 29 and 30 to the other pole of the source (not shown) of the electromotive force waves which are to be faithfully reproduced as sound waves. This source may be. for example, a vacuumtube amplifier fed from a telephone transmitter circuit. Upon the application of the electromotive force to the crystals, each crystal undergoes vibrations'about its principal axis, and the angular displacement which the bar 14 'un-,

dergoes is equal to the sum of the angular 'displacement of the upper basal plane of crystal 11 with respectto the lower ba al plane of'that'crystal and the angular dis-.

placement of the upper basal plane of crystal 12 with respect to the lower basal plane of that crystal, The vibration of the bar 11 causes the apex of the diaphragm to vibrate in the direction of the axis of the cone being a maximum.

formed by the diaphragm,'so that the diaphragm is set in yibration and causes in, the

surrounding medium, -for example the. air,

elastic vibrations of-the frequency of the electromotive force .waves applied to the crystals. If one ofthe crystals be disconnected from the source, the volume of sound produced-by the" diaphragm will be decreased, providing the voltage applied to the;

othercrystal remains the same; for the angular displacement of the bar 14: can not then exceed the angular displacement between the basal planes of the crystal ,to which voltage is applied. One crystal may be eti'ectively disconnected from the source by disconnecting lead 21 or lead2 l from the source. Since the impedance of each crystal is high, the impedance of the source,

such as a vacuum tubeainplifier, will often be more nearly eqllal to the impedance of the two crystals in p'arallelrthan'to the impedance ot' a single crystal, or. than to the v impedance of two crystalsconnected inseq ries. -Moreover, when the two crystals are connected in parallel-the tull voltage dc-1 liyered by the source 15, of 'COHISG, apphed .to each crystal, and further, it is not necessary to insulate the basal. planes of-one crys tal from those of theother, since they may all-be at the samepotent-ial.

The mass of the. base 13 shouldbe sufii.-'

ciently great to insure thatwhen the crystal structure 10 undergoes elastic vibrations due to the application of varying currents thereto, the lower surface ofv the crytsal 12 will remain firmly anchored and the displacement "of any part of the crystal structure 10 4 will be proportional to the distance-of that part from the lower end of the structure, the

displacement of the top'end of the structure For, even though the mass of the diaphragm be small, the reaction of the 1 air or other surrounding "medium,

when the diaphragm vibrates, tends to anchor the diaphragm and the topof the crystalstructurc and cause thedisplacement of the crystal structure about its axis to be greater at the. lower end of the tlXlStlltlIl at the upper-end, and if the mass of the base 13 be inadequate to overcome this tendency, the base rather than the diaphragm will vibrate, and the efliciency'with which the elastic vibrations of the crystal are transmitted to the I air will thus be reduced. The lighter the crystal structure the more important it is that the base be heavy,'if the reaction of the diaphragm against the crystal structure, and other factors, remain the same.

-. The loud speaking receiver may be used as a transmitter by applying sound waves to the diaphragm and taking ofi corresponding currents from the positive and negative poles of the crystal structure.

Figs. 3 and 4 show a loud speakersimilar in construction to that of Fig. 1, except that Inn y in Figs. 3 and 4 the crystal structure comprises four crystals 11, 12, 41 and 42 instead of merely the crystals 11 and 12. The crystals 41 and 42 form a pair fastened together and to the base 13' and the channel bar 14 just as the crystals 11 and 12 are fastened together and to the base and the channel bar in Fig. 1 or in Fig. 3. Preferably the four crystals are all connected in parallel, that is, with the four girdle or equatorial poles of the crystals electrical] connected to one pole of the source (not sliown) and all of the basal planes of the crystals connected to the other pole of the source. The crystals 11 and 12 act, as in Figs. 1 and 2, to give to the bar carrying the diaphragm angular displacement larger than either crystal alone would give it. The crystals 41 and 42 act similarly to the crystals 11 and 12, each pair of crystals tending to turn the bar 14' in the same direction as the other pair. Inasmuch as the upper basal planes of crystals 11 and 41 are rigidly united by means of the bar 14' and since the equatorial poles of both these crystals are charged synchronously from the same source of clectromotive force, the rotational displacement of bar 14 will correspond to the summation of the torsional forces exerted by the base of crystal sets 11, 12 and 41, 42. The force exerted on.the bar 14 is therefore the resultant of the torsional forces exerted by the two pairs of crystals, and consequently is greater than the force that would be exerted by either pair alone.

- By omitting from circuit any desired crystal or crystals, the amplitude of vibration of the bar 14', and the volume of the sound produced by diaphragm 15, can be correspondingly reduced. The device of Figs. 3 and 4 has the frequency range of its maximum responsiveness lower than has the device of Figs. 1 and 2, since the radius of gyration of the crystal structure of Figs. 3 and 4 is larger than that of the crystal structure of Figs. 1 and 2. However, the frequency range ofinaximum responsiveness may be diflferent for each of the four crystals in Fig. 3, so that the quality of the sound produced by the device may be altered by disconnecting any desired one .or ones of the crystals from circuit. It is pointed out here that, in Figs. 3 and 4, even when only one crystal is connected in circuit the frequency of maximum response of the loud speaker is affected by the presence of the other three crystals, both because of the resistance which they ofl'er to being strained and because of their inertia. Further, the effects, from the natural frequency of the loud speaker, of this resistance and this inertia will depend upon the relative position of the crystals.

Instead of mounting two pairs of crystals on the same diameter of the base, as in Figs. 3 and 4, one pair may be mounted to one side of a diameter and the other pair'to the other side, as in Fig. 5, in which 11 and 45 are intended to indicate either two single crystals mounted back to back, or two pairs or stacks of crystals with the pairs or stackmountcd back to back. It is not necessary that the number of crystals in each stack be the same, but it is convenient to have the stacks equal in height so that the bar which carries the diaphragm 1:) as shown in Fig. 3 may fit onto the tops of both of the stacks. Each stack will tend to giro the bar an angular displacement dependent upon the height of the stack, and the force exerted upon the bar by the two stacks will be the summation of the forces exerted by the individual stacks, and consequently will be greater than the force that either stack alone would exert. Because of the shape of the crystals, where the stacks are placed back to back the channel ban which carries the diaphragm 15 as shown in Figs. 1 to 4 can be narrower than it the stacks were. orientated in the same way or were placed face to face.

vl igs. t3 and 7 show a modification of the loud speaker of Figs. 1 and 2, in that the crystal structure comprising crystal 11 and 12 is mounted in a container which comprises a cylinder 51 closed at the top and a base 13 similar to base 13 but grooved as shown at 52 to receive the lower edge of the cylinder. The crystal structure is preferably cemented to the base and to the top of.the cylinder with cement. In assembling the crystal structure in the container, the crystal structure is cemented to the top of the cylinder 51, the groove 52 is filled with cement, cement is placed on the base where the bottom of the crystal structure is to rest, and the cylinder and the crystal structure are then pressed downwardly onto the base, and the cement at the bottom and at the top of the crystal structureallowed to set. Of course, before the cylinder has been cemented to the base, leads 21 and 2- (see Fig. 2), for connecting thegirdle poles of crystals 11 and 12 to the source of current for the loiul-speaker, should be brought out from the container, and the lead 28 (see Fig. 2), for applying potential to the lower basal plane of crystal 11 and the upperbasal plane of crystal 12, should be connected either to the cylinder 51, which is preferably of metal a few thousandths of aninch thick, or to the base. The electrical conductivity of the cement in groove 52 preferably should be sufficient for establishing electrical connection between the cylinder and the base. The leads 21 and 24 may unite before passing through the envelope of the container, so that only one lead need be brought through the envelope, and that lead should be insulated from the envelope, and should be sealed in the envelope so that the container will be air tight in order to better protect {til Ill)

the crystals :from change in humidity or other conditions of the air outside of the container.. The electrical connection between the basal planes'of the crystals 11, 12aand a pole of the source which supplies the currents for operating the loud speaker may be'made at any part of the cylinder 51 or thebase 13".

i The diaphragi'ir 15 .is attached to the top a of the -cylinder 51 with the axis of the diaphragm perpendicular to that radius of the cylinder top which passes through the point of attachment, so that twisting of the cylinder willccause the apex of the diaphragmto more in the direction of the axis ofthe diaphragm. The means for attaching the diaphragm to the cylinder top may be, for instance, like'that used to fasten the diaphragm to-the bar 14 in Figs. 1 and 2.

In the operation of the device of Figs,

6 and 7 'as a' loud speaker, when an alternating electromotive force is applied to the crystals the crystal structure, undergoes elastic vibratory twisting, and the cylinder 51 is thus caused to undergo elastic vibrat'ory twisting about itslongitudi-nal axis. T his twisting of the cylinder causes the apex of the diaphragm'15 to vibrate in the-direction of the axis of the diaphragm, and consequently the diaphragm produces sound waves corresponding to the e-lectromotive force waves applied to the 'crysta1s,

In order to improve the electrical connection between the pole faces ofthe crystals employed in the loud-speakers described. herein and the conducting surfaces or elec' trodes in contact therewith, these pole-faces are preferably coated with graphite.

Where the cement referred to above is made from sodium potassium tartrate in the man- .ner indicated, the cement after it has set,

is preferably moistened with any liquid containinggraphite or other conducting materlal where th:s can conveniently be done, by impregnating or paintlng the cement joints,

in order to improve, the electrical conductiv ity of the cement. The liquid applied to the surface will beabsorbed by the cement and will permeate it. w

Figs. 8 and 9show a form ofloud speaker wherein the crystals 61 and 62 of the type referred to above are secured end to .end, after the-fashion-in which crystals 11 and 12,

are secured end to. end in Figs. 1 and 2, but" with their adjacentba'sal planes electrically msulatedfrom eachotherby astrip of insulation 69 suclufor. instance as bakelite. The electrodes on these basal planes are preferablv of grid form, for example wire mesh, as described above, so that the basal planes may be cemented to the strip 69 with an electrodebetween eachbasal plane and the strip 69. This crystal structure-comprising the crystals 61 and 62 is mounted in a watch case form of-container comprising-the bowl' Lemmas shaped member 63 and the cap or cover attached thereto by any suitable means"; (not shown); The cap 65 carries a horn 64 and-a disc shaped diaphragm 66 which is clamped at its edges between a clamping ring 67 and 70' a shoulder on the cap. The member 63 con; sists of a'disc shaped part and a rin or flange ezitendingto one side of the periphery thereof and. coaxial with the disc shaped part. Tl1is ring shaped part is thickened, in

themaiiner indicated at 63', at opposite ends I of a diameter, so that the interior surface of the ring at each of these thickened parts is .a plane-surface containing a chord of thering, these two plane surfaces being parallel. ()no end of the erystalstructurecomprising crystals 61 and' 62.v is 'ceinentcd to'one of these .plane-surfacesand the other end of the crystal structure is cemented. to. the "other plane surface, each end of the crystal ,structure being provided. with an electrode of grid form as described above interposed be- ,of'a rod68, so'that elastic vibratory twisting of the crystals will cause the center ofthe. diaphragm, to vibrate in the direction of Ice the axis'of the diaphragm. The diaphragm,

the horn, the cap 65 'andtheclamping'ring 67: may be of any suitable materials, and although Figs. 8 and9 showa disc diaphragm vand a horn fortransmitting elastic. vibrations of the crystal-structure'to the air, it is clear that other means, for example aldia phragmof the form shown in the other figures of the drawing, may be used instead. WVith the .form of the invention shown in 11 Figs. '8 and'9, the crystals, although connected in parallel, are preferably oppositely connected electrically, in circuit. .That is,

one pole of the source of currents for operating the loud speaker should be connected to the girdle pole of one crystal and to thebasal' planes of the other crystal; and the other pole of the source should be connected to the other girdle pole andthe other basal planes. The wire connectionsto the crystals 12.

are indicated at- 75, 76, 77, 7-8, 79 and 80.

In the operation of this form of the inven-. tion as a loud speaker theelectromotive force wavesfrom thesource when applied to e the crystals, cause each crystal toundergo elastic vibratory twisting with respect to the principal axis of the crystals, and since one end'of each crystal isanchored-to the member 63 I the other ends of thecrystals undergo angular displacements,both crystals tending to turn the strip 69 in the same direction about the principal axis of the crystals. Therefore, the'strip 69 vibrates about this axis, and causes the center of the diaphragm 6G to vibrate in the direction of the axis of the diaphragm. It should be noted that the torques, rather than the displacements, due to the vibrating crystals are integrated for vibrating the diaphragm.

The diaphragms shown in Figs. 1 to 7 are intended to represent any suitable means for transmitting the elastic vibrations of the crystals to the air or other surrounding me dium, and although the conical diaphragm is the preferred means, it is clear that other forms, for example, the form shown in Figs. 8 and 9, may be used. Although the invention has been set forth with especial refer ence to its application to telephonic reception, it is applicable in various other fields, as for instance in the generation of electric currents in response to elastic deformation of piezo-electric bodies.

The invention is of course not limited to the materials specifically mentioned above, and, moreover, it will be obvious that the general-principles herein disclosed may be embodied in many organizations widely different from those illustrated without departing from the spirit of the invention as defined in the appended claims.

Certain broad features disclosed herein are claimed in application Serial No. 227,802, filed April 10, 1918, 1,495,439, May 27, 1924:) entitled Piezophony, and in application Serial No. 295,- 967, filed May 9, 1919, (now Patent No.

1,525,823, Feb. 10, 1925) entitled Piezo-elec-' trio transmitter, and my application Serial No. 740,746, filed September 30, 1924:, entitled Cement composition and method of preparation, claims a cement made from sodium potassium tartrate, and the process of making the cement.

The invention claimed is:

1. .In combination, a piezo-electric structure, means comprising a diaphragm for transmitting elastic vibrations between said structure and -a surrounding medium capable of propagating elastic vibrations, said means being so associated with said structure that said structure is capableof vibrating said diaphragm, and means associated with said structure for opposing the forces exerted by said diaphragm upon said structure when said diaphragm is undergoing vibrations.

2. A telephone instrument comprising two means, one a crystalline structure and the other a diaphragm so associated with said structure. that vibrations of either of said two means will be transmitted to the other and non-yielding means attached to sai (now Patent No.

vibration in a ponderable medium capable of transmitting elastic vibrations, and means comprising an elastic piezo-electric structure connected to said diaphragm in such manner as to be capable of causing a portion of said diaphragm at which said means is connected to vibrate in response to vibration of said structure, said means having a mass sufliciently large to insure that the forces transmitted between said diaphragm and said means when said diaphragm is undergoing said vibrations in said medium Will have no material eti'ect in determining what part of said means vibrates with the greatest displacement.

4. A telephone receiver comprising a piezo-electrie structure, means for setting up elastic vibrations in said structure, a diaphragm for producing sound waves arranged to be vibrated by said structure, and non-yielding reaction means attached to said structure for reflecting vibrations of said structure and said diaphragm and causing the elastic vibrations of said structure to be efiiciently transmitted to said diaphragm.

5. In combination, a diaphragm subject to vibration in a ponderable medium capable of transmitting elastic vibrations and a piezo-electric crystalline structure attached to a heavy base, said diaphragm being so associated with said structure that said structure is capable of vibrating said diaphragm in response to vibration of said structure, the mass of said base being suflicient to insure that the forces transmitted between said diaphragm and said structure when said diaphragm is undergoing said vibrations in said medium will not cause said base to be moved as a whole.

6. In a loud speaking telephone receiver, a piezo-electric structure comprising a sodium potassium tartrate crystalline body, means responsive to electric currents for causing said structure to undergo elastic vibratory twisting, a conical diaphragm for transmitting said elastic vibratlons of said structure to the surrounding air, a connection between said structure and the apex of said diaphragm for moving said apex in the direction of the axis of said diaphragm in response tosaid vibratory twisting of said structure, and a base to which said structure is rigidly connected, said base having sufiicient inertia to insure that the elastic vibrations of said structure are efliciently transmitted to said diaphragm.

7. A piezo-electric crystalline bod an airtight container therefor, a conica diaphragm and means comprising said, container connecting said body to the apex of. said diaphragm in such manner that elastic vibratory twisting of said body is capable of producing vibrations of said apex in the direction of the axis of said dia hragm.

8. A piezo-electric structure, a fibrous die-- phragm free at its periphery and subject to vibrations in a ponderable medium capable of transmitting .elastic vibrations, said dia- .phragm and said structure being so connected that vibrations of onewill be transmittedto the other, and a mass so attached to said structure and having such inertia as to render said structure capable of efliciently' 10. A piczo-elect-ric structure comprising a plurality of crystalline'bodies, and means for causing elastic strain of said structure, said crystalline bodies. being so arranged that the accompanying strains of certain of said bodies are physically integrated and the accompanying stresses of certain of said bodies are physically integrated.

11. A piezo-electric structure comprising two crystalline sod um. potassium tartrate bodies each having a principal axis and faces in which said axis terminates,-and means'for securing-said crystals to ether with two of said faces in opposing re ation. A

12. A piezo-electric structure comprising a plurality of crystalline bodies and a diaphra so associated with said structure that e astic vibratory twisting of said structure is capable of-causing vibration ofsaid dia hragm in the direction of the axis of sai diaphragm, said crystalline bodies being'so,'arrang ed that the twisting stress ex--v erted upon said structure'by said diaphragm when said diaphragm vibrates-is transmitted to said bodies. v

13. A piezo-electric structure comprising a plurality of sodium potassium tartrate opposing relation and crystalline bodies each having a principal axis and afacesin which said axis terminates, d and means for securing said crystals together.

in such manner that two of said faces are in two of said axes are in alignment.

14. A loud-speaking telephone receiver comprising two sodium potassium 'tartratc 'crystalsplaced endto end, and a diaphragm attached to thefree end of one' of said crystals".

.15. A piezo-electric structure comprising I a plurality of crystalline bodies, and means for-causing elasticivibratory twisting of each of said bodies with respect to a crystal axis of said'body, said bodiesbeing so arranged 9 "that the, accompanying twisting. strains .of

said bodies are physically integrated,

two means, one of said means comprising a piezoelectric crystalline structure and the other of said meauscomprismg a diaphragm and being so associated with said structure 'tl ltli) vibrations of either of said two means will be transmitted to the other, and a support to which said structure is rigidly attached, the mass 01' said support bein sufficient' to enable elastic vibrations structure to be eflici'ently transmitted to said other means, and the reaction opposed by 0? said said other 'means to being vibrated in response to elastic vibrations of said structure being of such magnitude that said elastic vibrations o-fsaid structure could not be efficiently transmitted to said other means in the absence of suflicient inertia in port. ,1 Y

17. In combination, a piezo-electric crystalline structure, means comprising adiaphragm for transmitting elastic vibrations between said structure 'anda surrounding medium ca able of transmitting elasticvibrations, said means being so associated with said structure that said structure is capable of vibrating said diaphragm in the direction of the axis of said diaphragm in response to vibratory twisting of said structure, and a base to wiichsaid structure is ri idly said supattached, sai base reacting against elastic vibrations of said structure. 0

18. Incombination, a piezo-electric structure, means capable of setting up elastic twisting vibrationsin said structure in re-' sponse. to varying electric currents, means comprising a diaphragm. for transmitting elastic vibrations between said structure and a surrounding medium capable of propagatingelastic vibrations, said last mentioned means being so associated with said structure that saidstructure is capable of vibrating said dia hragm in the direction of the axis of said iaphragni in response to said elastic twistingvibrations of said structure, and means associated withsaid structure for opposing. the twisting forces exerted. by said diaphragm upon said structure when said iaphragm is undergoing vibration in the direction of the axis of the diaphragm.

- 19. In combination, a diaphragm subject tovibration' in a ponderable mediumcapablc of transmitting elastic vibrations, and means comprising an elastic piezo-electrie structure connected to said diaphragm in such manner as to be capable of causing a portion-"of said diaphragm at which said means is connected to vibrate in the direction of the axis of said diaphragm" in response to elastic vibratory twisting of said structure, said means having a mass sufiicientl forces transmitte between said diaphragm and said' means when said diaphragm is undergoing said vibrations in said medium will have no material effect in determining 16, A telephone instrument comprising what part of said means vibrates with the greatest displacement.

large to insure that the of transmitting elastic vibrations, and a piezo-electrie crystalline structure attached to a heavy base, said diaphragm being so associated with said structure that said structure is capable of vibrating said diaphragm in the direction of the axis of said diaphragm in response to elastic vibratory twisting of said structure, themass of said base being sufiicient to insure that the forces transmitted between said diaphragm and said structure when said diaphragm is undergoing said vibrations in said medium will not cause said base to be moved as a whole.

21. A pieZo-electric structure, a diaphragm comprising a conical member for transmitting vibrations corresponding to sound waves, and means connecting said diaphragm to said structure for transmitting said vibrations between said diaphragm and said structure.

22. A. telephone instrument comprising two means, one of said means comprising a piezo-electric crystalline structure and the other of said means comprising a diaphragm so associated with said structure that vibrations of either of said two means will be transmitted to the other, and a base to which said structure is rigidly attached, said base reacting against elastic vibrations of said structure.

In witness whereof, I hereunto subscrlbe my name this 27th day of- February, A. D. 19:23.

ALEXANDER MoL. NICOLSON. 

